#include<cstdio>//uncle-lu
#include<algorithm>
template<class T>void read(T &x)
{
	x=0;int f=0;char ch=getchar();
	while(ch<'0'||ch>'9') { f|=(ch=='-'); ch=getchar(); }
	while(ch<='9'&&ch>='0') { x=(x<<1)+(x<<3)+(ch^48); ch=getchar(); }
	x = f ? -x : x;
	return ;
}

struct node{
	int x,y;
	friend bool operator<(const node a,const node b)
	{
		return a.y<b.y;
	}
};

node line[1010];
int F[1010];
int n;
int ans;

int main()
{
	read(n);
	for(int i=1;i<=n;++i)
	{
		read(line[i].x);read(line[i].y);
	}

	std::sort(line+1,line+1+n);

	for(int i=1;i<=n;++i)
	{
		F[i] = line[i].y-line[i].x+1;
		for(int j=1; j<i && line[j].y < line[i].x ;++j)
			F[i] = std::max(F[i], F[j] + line[i].y-line[i].x+1);
		ans = std::max(F[i], ans);
	}

	printf("%d",ans);
	return 0;
}
